Internal combustion engines convert chemical energy from a fuel into mechanical energy. The fuel may be petroleum-based, natural gas, another combustible material, or a combination thereof. Most internal combustion engines inject an air-fuel mixture into one or more cylinders. The fuel ignites to generate rapidly expanding gases that actuate a piston in the cylinder. The fuel may be ignited by compression such as in a diesel engine or through some type of spark such as the spark plug in a gasoline engine. The piston usually is connected to a crankshaft or similar device for converting the reciprocating motion of the piston into rotational motion. The rotational motion from the crankshaft may be used to propel a vehicle, operate a pump or an electrical generator, or perform other work. A vehicle may be a truck, an automobile, a boat, or the like.
Most internal combustion engines have a camshaft to operate the inlet and exhaust valves on the cylinders in the engine. A camshaft has cams or irregularly shaped projections on a shaft or rod. As the camshaft rotates, the cams turn the rotating motion into a reciprocating motion for operation of the valves. The crankcase usually rotates the camshaft through a cam gear.
Many internal combustion engines have a camshaft position (CMP) sensor near a target wheel mounted on the cam gear. CMP sensors generally produce an output signal in respond to the presence or interruption of a magnetic field. The output signal may be digital or analog and usually is proportional to the magnetic field strength. The target wheel usually has a disk shape with openings or windows along the circumference. The target wheel may have vanes or blades extending from a center hub. As the target wheel rotates, the windows or vanes pass through the magnetic field of the CMP sensor. The windows or vanes disrupt the magnetic field thus causing the CMP sensor to produce or change the output signal. A vehicle's on-board computer or electronics can determine the speed, position, and other operating parameters of the camshaft from the output signal. From the camshaft speed and position, the on-board computer or electronics can determine the engine speed and the position of the piston within each cylinder.
The CMP sensor usually is replaced when operating improperly. The CMP sensor may be replaced during engine repairs or maintenance even when working properly. Many internal combustion engines do not operate when there is no output signal from the CMP sensor. When the output signal is not present, the vehicle's on-board computer and electronics may generate a no-start condition to prevent operation of the engine. Service technicians can check operation of the CMP sensor using the vehicle's on-board computer, electronics, and tachometer, which may be unreliable given the no-start condition of the engine. Many service technicians replace the CMP sensor as part of a general diagnostic approach if an engine does not start. If the new CMP sensor does not address the no-start or other concerns, the old CMP sensor is not reinstalled even though it may work properly. The replacement of a CMP sensor that works properly may increase the operating and/or maintenance costs of the engine.